Being born between September and November doesn't guarantee you a longer life, but the odds are certainly in your favor. A new study of 1,500 centenarians - those who have lived at least 100 years - born between 1880 and 1895 has found that those with a Fall birthday live longer than their siblings or spouses.

Researchers from the University of Chicago compared these 100-year-old's birthdates with 12,000 data points from their family members, which were used to eliminate outside factors like lifestyle that could affect life span.

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"This is the first study which found month-of-birth effects on longevity by using a within-family analysis, which proves that month-of-birth effects are real, and are not related to differences between families," said Leonid Garilov, an expert on aging, mortality, and longevity at the University of Chicago, according to Discovery News. "The findings of this study support the idea of early-life programming of human aging and longevity."

The team found that most people who lived extraordinarily long lives had birthdays in September, October, or November. By contrast, a slight majority of people in the non-centenarian population were born in the first half of the year, reports The Week. In fact, three birth months - March, May, and July - had 40 percent fewer centenarians.

The reasons for this aren't clear, but the researchers suggest a few possible causes. In the late 1800s, food abundance was dependant on seasonal changes. The Fall harvest may have contributed to breast-feeding mothers eating healthier and transmitting more nutrients to their young ones.

Weather may also play a role. The relatively mild temperatures of Fall - as opposed to hot summers or cold winters - can also make babies more hearty, reports Fox News.

Though, today, these conditions may not still apply, it's worth noting that early experiences can have lasting effects on life span, researchers said.